The present invention relates to thermal energy storage compositions comprising macrocapsules or beads containing phase change materials (PCMs) and, more particularly, to macrocapsules containing microencapsulated phase change materials. Although the focus of the present application is directed to encapsulation of phase change materials, the procedure described herein can also be used to encapsulate a variety of materials, such as fragrances, pharmaceuticals, pesticides, oils, lubricants, and the like.
U.S. Pat. No. 5,415,222 to Colvin, et al. discloses a cooling garment, preferably in the form of a vest that contains pouches containing a phase change material. In one embodiment the cooling garment includes a honeycomb structure which is contained within the pouches and which contains a macroencapsulated phase change material and allows the escape of perspiration through the garment. The cooling garments are designed to permit evaporative cooling to occur and to contribute to the overall comfort of the wearer.
U.S. Pat. No. 5,290,904 to Colvin, et al. discloses a thermal shield which may include a phase change material in bulk, micro or macro encapsulated to provide enhanced thermal protection.
U.S. Pat. No. 4,911,232 to Colvin, et al. and U.S. Pat. No. 5,007,478 to Sengupta disclose the use of slurries of microencapsulated PCMs in thermal loops for heat transfer in systems which necessitate the use of more efficient thermal transfer fluids, such as systems in which large quantities of heat must be removed in short periods of time or systems in which there are system size restrictions which limit the volume of fluid which can be transported in the thermal loop. Such systems include lasers, electronic components, supercomputers, nuclear generators, etc.
U.S. Pat. No. 4,756,958 to Bryant discloses fibers and fabrics which incorporate microencapsulated PCMs. These materials exhibit enhanced thermal energy storage properties and can be manufactured into garments useful in extreme cold or extreme heat.
U.S. Pat. No. 4,513,053 discloses microencapsulating PCMs for incorporation into concrete or plastics.
The disclosures of the above-identified patents are incorporated herein by reference.
The present invention is directed to thermal energy storage compositions comprising macrocapsules containing therein a plurality of microcapsules and to methods for producing macrocapsules containing microcapsules. In accordance with some embodiments of the present invention, the microcapsules contain a phase change material.
In accordance with one embodiment of the present invention, a method for producing a macrocapsule containing a plurality of microcapsules therein comprises the steps of providing a plurality of microcapsules; suspending the plurality of microcapsules in a gelling agent solution thereby forming a suspension of microcapsules in the gelling agent. Suspension of adding the microcapsules as discrete drops to a crosslinking solution thereby crosslinking the gelling agent coating and forming discrete macrocapsules, and drying the macrocapsules.
Macrocapsules prepared in accordance with the present invention can be incorporated inside a coat, vest or other article for the purpose of absorbing body heat to increase the wearer""s comfort level and thus to increase the length of time that the wearer can engage in a physical activity. The macroencapsulated phase change materials can be used in a variety of products such as firefighting garments, hazmat suits, specialized clothing for foundry workers, armed forces, etc.
The macrocapsules of the present invention may be used in any application relating to the transfer and/or storage of heat. Specific examples include, but are not limited to, the use of these materials in HVAC systems and construction materials for residential and commercial buildings, home furnishings and automobile upholstery, heat sinks for computers, etc.
The macrocapsules of the invention have a particle size in the range of 1000 to 10,000 microns with a PCM payload of at least 50%, more particularly at least 75% and in accordance with some embodiments at least 80%. Conventional type microcapsules in this size range based on the reservoir type core concept present production problems. These problems in production are obviated by macroencapsulating high concentrations of microencapsulated PCMs.
In accordance with the present invention, microcapsules containing PCMs are added to a gelling solution and mixed thoroughly. After mixing, the gel/microcapsule mixture is dripped into a crosslinking solution to form discrete gel droplets. The droplets are removed from the crosslinking solution, rinsed with water and dried to a consistency of less than 1% moisture to produce macrocapsules according to the present invention.